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Geoelectrics

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Exam1
Vanerahal
Quiz by Vanerahal, updated more than 1 year ago
Vanerahal
Created by Vanerahal over 9 years ago
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Resource summary

Question 1

Question
Is the amount of pore space the most important factor controlling electrical conductivity?
Answer
  • True
  • False

Question 2

Question
What are the types of current flow?
Answer
  • Electronic, Ionic
  • Metallic, Aqueous

Question 3

Question
What are the two mechanisms by which we recognise the presence of an electrical inhomogeneity in the Earth?
Answer
  • By the generation of current circulating within a conductive body
  • By the generation of current not circulating within a resistive body
  • By generating currents that penetrate the boundary between two regions with di ferent electrical properties.
  • By generating currents that not penetrate the boundary between two regions with different electrical properties

Question 4

Question
The penetration of an electromagnetic field into the earth depends on:
Answer
  • Frequency of oscillation
  • Conductivity of the earth
  • Depth of investigation
  • Current flow paths

Question 5

Question
What is an inductive response
Answer
  • An inductive response occurs when current flows within the conductive region in proportion to its conductivity and the time rate of change of the applied magnetic field
  • An inductive response occurs when the currents will be distorted by the presence of the anomalously conductive body.

Question 6

Question
Specific exploration problems are characterised by speci c ranges in depth of interest leading to dif erent preferred frequencies. What are the range of depths and frequencies used in Oil and Gas exploration?
Answer
  • Frequency range: 1-10^-4 Hz Depths 10-1000 m
  • Frequency range: 100-10^-1 Hz Depths 10-100 m
  • Frequency range: 10-10^-3 Hz Depths 1-100 m

Question 7

Question
How is called a measure of how easy it is to produce an electrical polarisation within a material?
Answer
  • Galvanic Response
  • Inductive Response
  • Dielectric Constant
  • Permitivity of the material

Question 8

Question
The electrical properties of the rocks depend on...
Answer
  • The constituent minerals
  • Their mineral associations
  • Rock porosity
  • Fluid content
  • Permitivity
  • Dielectric constant

Question 9

Question
The main difference between resistivity-resistance and conductivity-conductance is that the former is related to the material and is a physical property of it (intensive property: does not depend on the system size or the amount of material in the system)
Answer
  • True
  • False

Question 10

Question
The materials can be classified according to their conductivity into groups. Select the groups:
Answer
  • Conductors, conductivity less than 10^5 S/m
  • Semi-conductors 10^-8 S/m < Conductivity < 10^5 S/m
  • Insulators Conductivity < 10^-8 S/m
  • Metallic conductivity less than 10^5 S/m
  • Sulphides 10^-8 S/m < Conductivity < 10^5 S/m
  • Aislators Conductivity < 10^-8 S/m

Question 11

Question
Mostly, the conduction nature in rocks is mainly electronic (Metallic conduction and/or Electronic semi-conductors)
Answer
  • True
  • False

Question 12

Question
The main difference between Metallic Conduction and Electronic Semiconductors is that the latter needs a much more significant amount of energy (heat) for the electrons to become dissociated from their home atoms
Answer
  • True
  • False

Question 13

Question
In terms of Metallic conduction, it can be said that the conductivity in metals depends on:
Answer
  • the number density of free electrons, the electron charge and the electron mass.
  • the number density of free electrons, the electron charge, the electron mass and the relaxation time

Question 14

Question
Fluid conductivity depends also upon temperature because the mobility of the ions in solution decreases with temperature.
Answer
  • True
  • False

Question 15

Question
Metallic conductors resistivity depends on temperature. When the temperature increases the conductivity of the metal decreases.
Answer
  • True
  • False

Question 16

Question
When an external electric fi eld is applied the electrons accelerate along the fi eld lines and a current is produced. This current would increase without limit if the electrons did not occasionally "collide" with the nuclei. The average time between collisions for a given electron is called
Answer
  • The relaxation time
  • Intrinsic time
  • Extrinsic time

Question 17

Question
The electronic semi-conductors are metallic materials just as native metals, the only difference is that they have a smaller number of free electrons with lower mobility.
Answer
  • True
  • False

Question 18

Question
Electronic semi-conductors need a signi cant amount of energy for the electron to become dissociated from their "home" atoms. One source of this is heat, the number of conduction electrons in these type of material depends on: Energy required to free an electron, Boltzmann Constant, and the absolute temperature So it can be concluded that:
Answer
  • For semiconductors a higher temperature results in more free electrons and therefore a higher conductivity.
  • For semiconductors a higher temperature results in more free electrons and therefore a lower conductivity.
  • For semiconductors a higher temperature results in less free electrons and therefore a higher conductivity.
  • For semiconductors a higher temperature results in less free electrons and therefore a lower conductivity.

Question 19

Question
It is possible to obtain movement of ions within a solid due to imperfections
Answer
  • True
  • False

Question 20

Question
In terms of Aqueous Electrolytes, the conductivity will depend on:
Answer
  • Amount of water present
  • Salinity
  • Temperature
  • Connectivity
  • Archie's law
  • Cementation factor

Question 21

Question
Archie’s Law: It is a purely empirical law attempting to describe ion flow (mostly sodium and chloride) in clean, consolidated sands, with varying intergranular porosity. Electrical conduction is assumed not to be present within the rock grains or in fluids other than water. So it can be said that the variables within the equation are:
Answer
  • An empirically defined constant
  • the cementation factor
  • Resistivity of the Aqueous solution
  • Porosity
  • Rock's bulk resistivity
  • Formation factor

Question 22

Question
What happens to Archie's law when part of the pore space is filled by air, natural gas, carbon dioxide or petroleum (insulators) ??
Answer
  • The equation remains the same
  • an empirical constant is added
  • Boltzmann constant is added to the equation
  • the volume fraction of pores with water power to the saturation exponent is added

Question 23

Question
The tortuosity is defined by the relation between the average length of the path through the crack and the length of the rock lc/l
Answer
  • True
  • False

Question 24

Question
The diminution ratio is the division between the cross-section area of the crack and the cross-section total area
Answer
  • True
  • False

Question 25

Question
Is a measure of the void (i.e., "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0 and 100%
Answer
  • Porosity
  • Crack
  • Joint

Question 26

Question
The electric permittivity is defines as...
Answer
  • a measure of the degree to which a given material becomes polarized.
  • electric dipole moment per unit volume
  • the amount of charge which is separated and the distance through which it has moved

Question 27

Question
The relative dielectric constant (Er or K) can be defined as...
Answer
  • the ratio of the material's permittivity to the permittivity of free space
  • the subtraction of the material's permittivity to the permittivity of free space
  • the multiplication of the material's permittivity to the permittivity of free space

Question 28

Question
What are the most important values in terms of relative dielectric constant
Answer
  • Water and Soil
  • Basalt, Coal Dolomite
  • Limestone, Granite Quartz

Question 29

Question
When the current flows more easily in some direction than in others is called Anisotropy
Answer
  • True
  • False

Question 30

Question
The longitudinal resistivity is always greater than the transverse resistivity.
Answer
  • True
  • False

Question 31

Question
The anisotropy coefficient SQRT(RT/RL) >= 1
Answer
  • True
  • False

Question 32

Question
Types of anysotropy
Answer
  • Azimuthal anisotropy (Dipping layers, Dominant set of vertical fractures)
  • Depth dependant anisotropy (the nature of the fracture fill changes with depth)
  • Transverse
  • Longitudinal

Question 33

Question
The main difference between IP and SP is that the former is mainly used to determine massive ore bodies whereas the latter is mainly used to determine disseminated ore bodies
Answer
  • True
  • False

Question 34

Question
Select the main uses of the SP method
Answer
  • Presence of massive ore bodies
  • Sulphide mineralization
  • Groundwater
  • Geothermal
  • Geological mapping
  • Chargeability

Question 35

Question
What is the cheapest and simplest method to apply? (In terms of near-surface geophysics)
Answer
  • SP
  • IP
  • ITS
  • Seismic Refraction
  • Gravity
  • GPR

Question 36

Question
The sign of the potential is an important diagnostic factor in the interpretation of SP anomalies. What kind of mineral potentials are expected for negative anomalies of hundreds of mV
Answer
  • Sulphide ore bodies, Graphite ore bodies, Magnetite, coal and manganese
  • Quartz veins, pegmatites

Question 37

Question
In mineral exploration the components of the SP are called the Mineral Potential and the "Background potential" What are the uses of the latter?
Answer
  • Massive ore bodies
  • Disseminated ore bodies
  • Geothermal research
  • Hydrogeological research

Question 38

Question
What type of electric conduction occurs in very weakly conducting materials (or insulators) when an external alternating current is applied, so causing atomic electrons to be shifted slightly with respect to their nuclie.
Answer
  • Electrolytic
  • Electronic
  • Dielectric

Question 39

Question
How is called one of the main groups of SP that are generally of the order of mV and mainly arise due to water circulation, small mineral quantities, biologic and topographic ef ects (human activities may also produce SP signals)
Answer
  • Electrokinetic Potential
  • Background Potential
  • Diffusion Potential
  • Mineral Potential

Question 40

Question
How is the called one of the main groups of SP that occur in regions of anomalous concentrations of sul fide ores (also near graphite) and can be of the order of hundreds of mV or even V.
Answer
  • Electrokinetic potential
  • Diffusion potential
  • Mineral potential
  • Background potential

Question 41

Question
Buried sulphide masses are known to cause SP anomalies. In terms of the effect observed and the physical cause of this effect. Which of the following is true?
Image:
0a5ff6f3-77cb-40dd-9076-86b96b1c26f9 (image/png)
Answer
  • Groundwater is thought to be common factor responsible for SP. The potentials are generated by the flow of water by water acting as an electrolyte and as a solvent of different minerals.
  • A negative anomaly of hundreds of mV is expected
  • A postive anomaly of hundreds of mV is expected
  • One proposal can explain all SP observations
  • 1. Above water table: dissolved electrolytes gain electrons from the ore body and are reduced. 2. Below the water table: an oxidation reaction occurs transferring electrons back to the ore body. 3. Electrons are then conducted through the ore body completing the circuit.
  • It is possible that only the presence of variable redox conditions within the subsurface is required to generate large SP anomalies, without need of a subsurface conductor to "close the circuit."

Question 42

Question
The SP potentials tend to increase in positiveness with the direction of water flows as the electric charge flows in the opposite direction.
Answer
  • True
  • False

Question 43

Question
How is called the mechanism by which SP anomalies are generated that is useful to map subsurface barriers or conduits of flow. (These are generated by the flow of aqueous electrolytes through narrow channels (pores))
Answer
  • Electrokinetic or Streaming potentials
  • Diffusion
  • Electrolytic

Question 44

Question
In practice, to ensure good ground contact in the field and to obtain reliable measurements, What sort of actions should be taken?
Image:
8702643c-a12f-49bf-9ff6-62a0add2ad27 (image/png)
Answer
  • Porous-pot electrodes
  • Non-porous electrodes
  • The Resistance of the voltimeter must be large enough 10^8 Ohm
    Image:
    a5ff6d8c-8724-484b-b8b1-9d07e0275042 (image/png)
  • The electrodes should be kept dry and shaded to ensure good ground contact (when the fixed electrode is used)
  • The electrodes should be kept wet and shaded to ensure good ground contact (when the fixed electrode is used)

Question 45

Question
There are diff erent possible arrangements in which the equipment can be deployed?
Answer
  • Static array
  • Fixed Spacing
  • Fixed Electrode

Question 46

Question
The advantage of using a fixed spacing SP survey is that you can use a shorter wire and the reduced importance of telluric currents (generally long-wavelength currents induced in the ground by geomagnetic fluctuations).
Answer
  • True
  • False

Question 47

Question
The major advantage of using a fixed spacing SP survey is that generally needs to operators to moves the system
Answer
  • True
  • False

Question 48

Question
The gridded measurements in the SP fixed spacing survey should ultimately form a closed loop and the sum of all potentials within that loop should equal zero if not the remainder represents an error and should not be distributed among the readings
Answer
  • True
  • False

Question 49

Question
The main disadvantage of using a fixed electrode system (sp) is that system include generally more measurement errors and that is not easy to perform by a single operator
Answer
  • True
  • False

Question 50

Question
The main advantage of using a fixed electrode system is that the larger separation between electrodes does not allow telluric currents to influence the results
Answer
  • True
  • False

Question 51

Question
SP can be easily executed on Ice.
Answer
  • True
  • False

Question 52

Question
Problems associated with acquiring SP data and things that must be taken into account:
Answer
  • Electrode polarization
  • Rain (Ground-contact strength and ground conductivity)
  • Telluric variations (Daily drift variations)
  • Artificial sources of electricity in the surroundings (or in the vicinity)
  • A shift in the equipotential lines in relation to an ore body (current will flow preferentially in the less resistive unit.)
  • Longness of the wire

Question 53

Question
the observed current and potential due to a single source in a half space is identical to that from the method of images inspired model of two sources in an in finite space.
Answer
  • True
  • False

Question 54

Question
Consider a vertical, infinite length, ellipsoidal ore body. Sketch the expected SP anomaly profile over this body
Image:
4984d4ed-16e3-4be3-883e-e9ec5107b906 (image/png)
Answer
  • A vertically body will have no positive anomaly
  • A vertically body will have a positive anomaly
  • the anomaly peaks are not simply located above the poles
  • the anomaly peaks are simply located above the poles
  • For a dipping body, the negative anomaly associated with the shallower, negative pole is much more pronounced
  • For a dipping body, the negative anomaly associated with the shallower, negative pole is much less pronounced
  • A vertically body will have a negative anomaly that will be centered on the negative pole (in an homogeneous medium).
  • A vertically body will have a positive anomaly that will be centered on the negative pole (in an homogeneous medium).

Question 55

Question
For a tilted ore body how can you determine the depth to the sink
Image:
d95730e7-6419-4d6b-a8fe-ea2819b9c119 (image/png)
Answer
  • From the half-width of the anomaly profile x1/2=h0.73
  • From the half-width of the anomaly profile x1/2=h0.766

Question 56

Question
For a Vertically ore body (finite length l) how can you determine the depth to the sink
Image:
ab7fc2b9-95fe-4f43-bd92-b1698ad29934 (image/png)
Answer
  • From the half-width of the anomaly profile x1/2=h0.73
  • From the half-width of the anomaly profile x1/2=h0.766

Question 57

Question
Is the method of the ratio and the method of the Vmin give the true position of the ore body
Answer
  • True
  • False

Question 58

Question
When the profi le is drawn the reference (zero) potential needs to be set as the value for which the potential becomes constant far from the body, this process is helped by a good lateral extent of measurements and a low level of noise.
Answer
  • True
  • False
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